Steady-state and transient thermal effect of alkane-grafted Ti3C2Tx MXene

Surface functionalization provides an effective strategy for regulating the thermal transport and ultrafast carrier dynamics of MXene materials. However, the underlying coupling mechanism between alkane grafting, phonon scattering, and non-equilibrium energy dissipation remains insufficiently understood. Herein, we investigated the steady-state and transient thermal effects of alkane-grafted Ti3C2Tx MXene thin films through Raman spectroscopy, infrared optical spectroscopy, thermal transport measurements, and femtosecond transient absorption spectroscopy. Raman and AFM images demonstrated that long carbon-chain grafting induced enhanced local structural disorder, out-of-plane bending, and edge wrinkling features. Compared with Ti3C2Tx MXene, alkane-grafted Ti3C2Tx-C8H18 and Ti3C2Tx-C12H26 exhibited enhanced infrared absorption together with suppressed thermal transport behavior. In particular, extraction of the absorption coefficient, complex refractive index, and dielectric function further revealed that Ti3C2Tx-C12H26 MXene exhibited the highest average infrared absorptance of approximately 70%, together with an enhanced absorption coefficient, increased imaginary refractive index, and strengthened dielectric loss capability, indicating significantly improved infrared energy dissipation after long-chain alkane grafting. Meanwhile, its thermal diffusivity decreased to 7.57 mm2/s, while the specific heat capacity increased to 1.35 J/(g K), demonstrating its thermal energy storage capability. Femtosecond transient absorption measurements revealed faster carrier relaxation with increasing alkyl-chain length. The fast relaxation component decreased from 4.49 ps for Ti3C2Tx to 2.24 ps for Ti3C2Tx-C12H26. The slow relaxation component also decreased from 1510.86 to 491.26 ps, indicating more efficient local excited-state relaxation and energy dissipation in alkane-grafted Ti3C2Tx MXene. Our results demonstrate that long-chain alkane grafting effectively modulates thermal transport and ultrafast carrier dynamics in MXene thin films, providing a promising way for advanced photothermal conversion and infrared response devices.